How to start a 1999 Yamaha YZ400

I recently bought a 1999 Yamaha YZ400. It was in great condition but had been standing for a year and a half and wouldn't start, unless you run started it. Kick starting it was not an option. I bought in on the spot.

Before figuring out what was wrong, I did some investigation on the Internet. It quickly became clear these bikes are tricky to start even when they're in good tune. After some reading, this was my plan of action:

1. Try all the various techniques suggested to make sure the problem is not with me, that there is an actual problem with the bike.
   
2. Clean the air filter. I didn't believe this would solve the problem, but if you're struggling already you need all the help you can get.
   
3. Check the spark plug.
   
4. Drain the old fuel from the bike and replace.
   
5. Clean the carb.
   

If this didn't work, this bike was going to need some professional attention. So...

Techniques to start the bike:

• Never, ever touch the accelerator.
  
• Open the fuel tap.
  
• Pull the decompression lever in and kick through 10 times to clear everything. If I don't do this, the bike just won't start, no matter what I do.
  
• Kick the kickstarter to where it locks.
  
• Push the decompression lever in and carefully and slowly push the starter past the lock.
  
• Reset the kickstarter to the top of its arc and kick the bike. Later on, once the bike was running it seemed the best way to kick was a consistent kick from as high as you can go to as low as you can go. Not short, fast kicks. More a longer consistent arc from top to bottom.
  
• If the bike doesn't start within 5 kicks, repeat from step 3.
  

That didn't work, so I tried the following variations:

• Choke out, choke in.
  
• Hot start on, hot start off.
  
• Turned the idling speed adjuster 1 turn up every 10 tries with each of the combinations tried. Turned it back to original position once I'd tried everything. I could only do this after I'd removed and cleaned the carburettor but if you can do this from the start, try it.
  
• Last try was to "prime" the carburettor by turning one quarter and holding like that for 10 seconds. You have to try this last, if you try it any earlier you might flood the bike and then you're stuffed.
  

No luck, so on to next step.

Clean the air filter

Remove the seat, you'll be looking down into the airbox. Unscrew the screw securing the air filter and remove. Remove the sponge from the air filter frame. I've always washed in petrol so that's what I did. I decided not to cover with air cleaner foam, I would do that once I'd managed to start the bike.

I wasn't expecting any difference but tried to kickstart the bike just in case. No luck, so on to next step.

Check the spark plug

Before I say anything further, just let me say I wish I could lay my hands on the engineer at Yamaha that decided to put the spark plug in a deep hole right under the frame. Apparently you can buy a special tool to remove the spark plug. If you can find one, buy it. I didn't have one handy, so had to make a plan.

• Remove the seat.
  
• Remove the fuel tank as follows.
  
  • Unclip the fuel hose from the fuel tap. Use a screwdriver to push it out, don't pull on it.
    
  • The radiator shrouds are fixed to the radiator. Remove those screws.
    
  • With a long socket, remove the screws attaching the tank to the frame, both sides.
    
  • Lift the tank.
    
• You'll see there's a hose running into the head next to the spark plug wire. If you don't clip that out and push it to one side, you're going to struggle.
  
• Pull the plug wire out. You're now faced with a d-e-e-e-e-p hole. The plug is at the bottom.
  
• Now, if you have that special Yamaha tool, I imagine this must be quite easy. I didn't, so here's what I did.
  
  • Make sure you have a 16mm plug socket, a 75mm socket extension (shorter than +/-70 or longer than +/-75 and I reckon you're going to have problems) and one of those magnet on an aerial retrieval things.
    
  • Drop the plug socket into the hole.
    
  • Drop the socket extension into the hole.
    
  • Clip the extension into the socket (both are already in the hole when you do this).
    
  • Attach your socket spanner to the top and start unscrewing the plug, until it's fully screwed out.
    
  • Unclip and remove the socket spanner (the lever part at the top).
    
  • Push a screwdriver onto the top of the plug socket so it can't move. Pull the socket extension out of the plug socket.
    
  • Use the magnetic thingy to first remove the extension, then the plug socket, then the actual spark plug.
    
• Push the plug into the plug wire. Hold against the frame and kick start. You should see a healthy blue flame. If not, replace the spark plug.
  

In my case, the spark plug was fine so I put it back in by reversing the steps above.

Drain the old fuel from the bike

I removed the fuel line into the carburettor and opened the fuel tap on the tank. I let the fuel flow into bottles, to be disposed of later. The fuel looked all wrong, it was dark purple in color and the fuel that spilled on the floor had a gel like texture. I'm thinking the previous owner had probably added some additive to the fuel. However, a year and a half in storage and it was definitely not kosher any more.

Based on this, I decided to remove and clean the carburettor. However, if I hadn't, I would probably have just unscrewed the big silver screw on the bottom of the carb so the fuel could drain from there. (Don't know if this is maybe the wrong place to do it, but it would definitely drain the carb).

Left everything disconnected and proceeded to remove the carb.

Removing the carburettor

Before I start, a warning (I only figured this out later). When you remove the throttle cables, idling adjuster and pilot jet, make a note of their current settings. You're already struggling to start the bike, you don't want to inadvertently change the settings and add that to your problems.

• For the throttle cables, note or mark where the front screws were set to. If possible try to not touch them at all and remove by unscrewing the back screws (closest to the handle bars) only.
  
• In my case the idling adjuster screw was dirty so couldn't be set any more. I screwed it out and cleaned it. When I screwed it back in, I had a sort of an idea of where it was but it took some trial and error to get the idling speed set correctly after everything had been fitted again. Trust me, mark its position when you remove it and set it back to that when refitting.
  
• The pilot jet is normally screwed in and out through the hole in the bottom of the carb. After I had cleaned the carb, I screwed this in nice and tight, and effectively set the carb mixture extremely lean. It's supposed to be anything between .5 and 2 turns out, screw it in and count the rotations to see how far it was set out. Make a note and only then remove it. When you refit it, screw it in completely and then unscrew as per your notes.
  

I didn't document removing the carb, but did document refitting it. For removal, just repeat the steps from last to first. Note – the brown hoses around the carb do not need to be removed to remove or refit the carb. Just remove them with the carb, they don't plug in anywhere.

1. Clear the area you're going to be working in, make sure it's clean and there is enough light.
   
2. I'm assuming the tank is still removed. If not, remove as per above.
   
3. Remove the rags you pushed into the air box opening and opening to the engine.
   
4. Clip the pipe across the frame off (the one from the hot start to the other side of the frame). Clip off on the engine side, not the hot start side.
   
5. Use a screwdriver to leverage the pipe off.
   
6. Tuck the pipe from the air cleaner behind the frame to make some space.
   
7. Push the outlet side of the carb into the pipe from the engine. The pipe has a notch cut into it, make sure the carb slots into that notch. Make sure the carb is securely inserted, then fasten the clip.
   
8. Plug the electrical plug on the top of the carb into its matching socket on the frame.
   
9. Reconnect the overflow pipe on the bottom of the carb and fasten its clip. Route it through the square bracket on the frame so overflow doesn't flow onto any parts of the bike.
   
10. If the throttle cables are cable tied to any other hoses or wires, break the cable ties so you can move them around a little bit easier. You'll cable tie them back later.
    
11. Unplug the spark plug wire and move it out of the way.
    
12. Open the kickstart for more room.
    
13. Refit the accelerator cables (both of them). Rotate the throttle on the carb to fully open to make it easier to refit them.
    
    1. Note – the petrol tank should not be plugged into the carb yet. If it is, disconnect it, you're going to be flooding the carb while refitting the accelerator cables.
       
    2. If you were clever, you made a note of where the cables were set to before you removed them when you were removing the carb. Set them back to those settings.
       
14. Close the kickstart.
    
15. Screw the blank panel that is fitted over the accelerator cables back in.
    
16. Push the spark plug wire back in.
    
17. If you remove cable ties from the throttle cables, cable tie the throttle cables back into place.
    
18. The pipe from the airbox is tucked behind the frame. "Untuck" it and push the carb into the pipe from the airbox. Make sure it's pushed in properly, using a screwdriver if necessary. Tighten the clamp.
    
19. Refit the petrol tank.
    
20. Refit the seat.
    

Cleaning the carburettor

In my opinion, you don't have to touch the top of the carb. So...

• Removing the carb is a schlep, so while it's out really make an effort to ensure it's clean and works before you refit it.
  
• Unscrew the bottom part of the carb. It's held in place by 3 Allen key screws.
  
• Remove the float by removing the bar that keeps them in place.
  
• Once the float has been removed, remove the plastic thingy around the needle chamber.
  
• Unscrew the two jets with a screwdriver.
  
• Unscrew the pilot jet (the long screw that exits in the carb chamber). Remember to screw in first and count how many turns out it has been set. When you refit, you have to screw it back out the same number of turns, unless you're strong on carburettor tuning.
  
• Clean everything using petrol or (better) carb cleaner.
  
• Make sure there is absolutely no dirt in the jets by peeking through them. Blow through them and use a strand from a wire brush to remove any dirt you can see. By the way, this was my problem, the gooey petrol in the bike had clogged the low speed jet (the smaller one).
  
• Make sure the needle and its chamber is clean (you can see how this works by turning the accelerator).
  
• Check if the idling screw turns. If not, remove and clean but make a note of what it was set to before you remove.
  
• Everything nice and clean? Re-assemble the carb and refit (as per above).
  

In my case, the bike started! Success! However, I didn't know what the pilot jet was for so screwed it in completely. The bike was now running lean and thus very rough, with a backfire now and then for full effect. J

Guess what? You need a special tool to set the pilot jet while the carb is on the bike. More about that later, for now I was happy that the bike was at least running.